Update runC tests to include stdio and non-sleep processes

[beweedon]

Due to a bug I wasn't able to track down, container processes would occasionally exit at random in the test suite. This couldn't be reproed in any other environment than the tests. A workaround was to use only sleep processes in the runC tests. However, some combination of GCS and runC updates seems to have fixed the bug. The tests should now be expanded to include other types of processes than sleep.